This invention relates to transmission and transaxle assemblies for vehicles such as lawn and garden tractors and lawn mowers and, more particularly, to a dual input, constant mesh transmission/transaxle assembly which allows infinitely variable forward, neutral and reverse output speeds through totally mechanical means and without the need for a clutch when shifting between forward, neutral and reverse.
Conventional lawn and garden tractors, lawn mowers and other small vehicles incorporate transmissions or transaxles which typically provide several forward and at least one reverse speed as well as neutral outputs. Such vehicles are usually equipped with brake pedals, clutch pedals and shifting mechanisms which require the clutch to be depressed before any change in speed or direction. In some instances, double clutching or complete stopping of the vehicle is necessary before shifting can be achieved. This is especially difficult for women and children who use such machines. If such vehicles are operated on hills or slopes, the necessity of clutch depression can allow the machine to roll down the slope unexpectedly. At a minimum, a substantial level of coordination is required to operate vehicles using conventional clutch and shift mechanisms.
As an improvement to conventional clutch shifting transmissions, various types of variable speed transmissions have been developed which provide operation through a conveniently located single lever which merely need be pushed forward to move the vehicle in the forward direction, or pulled backward to reverse the direction of movement. The farther forward the lever is pushed, the faster the vehicle travels and vice versa.
One form of variable speed transmission now in use is a hydrostatic transmission in which a fluid drive is coupled to a conventional gear train for operation through the above-type single lever control. Such hydrostatic transmissions are relatively inefficient, especially under high heat conditions, require greater amounts of horsepower which would otherwise be available for mower or other implement operation than with other direct drive transmissions, and are relatively expensive to manufacture and install. Moreover, such hydrostatic transmissions are typically available only with horizontal drive shaft input which limits the tractor/mower configurations in which they can be installed.
Another type of variable speed transmission is a friction drive in which a traction wheel is engaged with a drive disk and is moved radially or across the center of rotation of the drive disk to vary the driven speed and/or the driven direction. Such friction drives, however, are unable to transfer large torque and, therefore, slip within certain speed or load ranges. Moreover, such systems require frequent servicing and lack reliability.
Accordingly, the need was apparent for a variable speed transmission/transaxle which would allow variable speeds in forward, neutral and reverse yet provide simple operation, preferably without the use of a clutch, through a single lever. It was also desired to have such a transmission/transaxle accommodate vertical drive shaft engines which are typical in lawn and garden tractor, lawn mower and other small vehicle installations, be inexpensive yet reliable, and eliminate inefficient power transfer typically encountered in conventionally known hydrostatic, friction or other variable speed drive units.
In addition, it was desired to provide a compact, well lubricated assembly which would require minimal maintenance and provide efficient lubrication throughout.
The present invention was conceived and designed in recognition of and as a solution for these and other problems.